This application claims the priority of German patent document 101 23 2373, filed May 12, 2001 (PCT International Application No.: PCT/DE02/01617, filed 4 May 2002), the disclosure of which is expressly incorporated by reference herein.
The invention relates to a nondestructive ultrasonic testing method and apparatus for detecting, assessing and localizing defects, with respect to a test region of a structural part.
According to the present state of the art, nondestructive testing methods are used to detect an incipient defect or to follow a developing defect of structures or structural parts, for example, in a vehicle such as an airplane (that is, for checking its structural integrity). In order to check the integrity of structures or structural parts, even when using nondestructive testing methods according to the state of the art, it may be necessary to disassemble the structure or structural parts to be checked, so that they can be made accessible for testing by the testing device. However, such disassembly requires considerable expenditures of time and resources.
From the lecture “Qualification and Validation of New Saphir-UT-Technology” at the 1st European Conference on Nondestructive Testing from May 26 to 29, 1998 in Copenhagen, a nondestructive ultrasonic testing method is known in which highly efficient eddy-current or ultrasonic sensors are temporarily coupled to the component surface. (The most efficient ultrasonic sensor types include, among others, so-called ultrasonic group radiators which have several jointly operated ultrasound sources, preferably in the form of piezoelectric elements). An ultrasonic excitation of the structure emanates from the ultrasound sources, which are controlled by way of an electric excitation. The ultrasonic excitation propagates as a structure response or sound field through the structural component to be tested and is partially reflected by inhomogeneities that may exist in the structure. The sound field reflected at such inhomogeneities can be received by sensors assigned to the ultrasonic group radiators, and converted to an electric signal in order to detect these inhomogeneities in the structure. In this case, the excitation takes place such that the sound field emanating from the group radiator has the shape of a lobe and thus has a preferred direction. The lobe can be focused at a variable distance. In this manner, inhomogeneities can be imaged in a location-resolving image.
This known imaging ultrasound method has the disadvantage that it is very costly in terms of equipment-related expenditures. The number of ultrasound sources that is necessary depends on the required resolution and range; it may comprise 8, 16, 32 or more channels which must be operated simultaneously. For this purpose, a high-expenditure high-frequency electronic system is required for each channel, such as an electronic system for changing between the transmitting and receiving operation; an electronic amplifier system on the controlling and receiving side; an electronic filtering system; a high-frequency analog-to-digital converter of a high bit resolution; as well as a high-expenditure electronic control system in order to achieve a swivelling and focusing of the sound field by a phase-shifted and amplitude-modulated control.
Another disadvantage of the method according to the state of the art is that the quality of the image, in addition to physical parameters (wavelength, ultrasonic wave velocity in the material, damping in the material, etc.), also depends on precise positioning of the sensors. This is particularly uncertain at locations of the structure which are difficult to access by means of radiators and sensors, so that the shape of the structure impairs the precision of the method. As a result, an exact comparison cannot be made between two test results (ultrasonic images) because the positioning generally varies between two tests.
In addition, specifically at those locations which are difficult to access, it is required to expose the surface of the structural part, which results in very high expenditures.
It is therefore an object of the invention to provide a nondestructive testing method and apparatus for the detection, assessment and localization of defects, which achieves high reliability in the test result, with reduced expenditures.
This and other objects and advantages are achieved by the nondestructive ultrasonic testing method and apparatus according to the invention which are suitable for testing structures, particularly those made of metals or fiber composites as well as mixed forms made of these materials. Depending on the material to be tested, the invention is especially suited for detection of defective points in the structure which are caused by corrosion, deformations, fiber ruptures, cracks or delaminations.
In contrast to the described state of the art, the method according to the invention eliminates the need for a focusing and a phase shift of the electronic excitation of the structure to be tested by means of an ultrasound source. The corresponding electronic expenditures are thus eliminated, so that the invention permits an imaging ultrasonic testing at considerably lower expenditures than according to known methods.
Furthermore, permanent application of the ultrasonic elements (that is, of the transmitters and receivers, provided according to the invention) achieves improved coupling of the ultrasonic excitation into the material, increasing their range in comparison to the state of the art. Such permanent application can be performed, for example, by gluing or soldering, or by a fixing device.
Another advantage of the invention is that the positions of the transmitters and receivers are constant between two time-shifted tests, because these are permanently arranged on the structure. As a result, an exact comparison of the measuring data of different measurements can be carried out.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.